An autofocus lens with large depth of field and high resolution

Abstract

The present invention discloses an autofocus lens with a large depth of field and high resolution. The lens is composed of a front lens group with positive optical power, an aperture, a middle lens group with positive optical power, and a rear lens group with negative optical power, from the object plane to the image plane. The aperture and the middle lens group are driven by a voice coil motor to move synchronously back and forth along the optical axis to achieve autofocus. The advantage is that high resolution and low distortion of the autofocus lens can be achieved by reasonably optimizing the optical power and selecting specific optical parameters. In combination with the voice coil motor, the lens volume can be effectively compressed and the cost can be reduced while achieving high-quality imaging within a large depth of field. Compared with traditional autofocus lenses and liquid autofocus lenses, the autofocus lens of the present invention has higher resolution, smaller volume, higher autofocus accuracy, and a larger depth of field.

Description

Technical Field

[0001] The present invention relates to an optical imaging lens, in particular to an autofocus lens with large depth of field and high resolution. Background Art

[0002] Scanners are widely used in a variety of fields, including retail, logistics, warehousing, and industrial production. As these applications continue to expand, market demands for scanner performance are also increasing: They require ultra-long working distances, extending from close-range scanning of a few centimeters to tens of meters or even further; efficient recognition capabilities, enabling rapid identification of high-density barcodes or QR codes at long distances, clearly identifying barcodes at the edges to reduce misread rates; and lightweight devices, achieving superior scanning performance with a more compact size, lower manufacturing costs, and lighter optical components.

[0003] To meet these requirements, some traditional scanners combine two fixed-focus lenses to expand their scanning range. However, these are large and the scanning range is insufficient to meet the requirements. Other scanners use autofocus optical components and mechanical methods (such as stepper motors) to achieve a larger scanning range. This solution is costly, bulky, and slow, and can also degrade image quality over time due to mechanical wear. Some devices, such as those described in Chinese Invention Patent Application No. CN202311154728.5, use a voice coil motor (VCM) to drive the entire lens to achieve imaging at varying distances. However, these devices exhibit poor resolution and distortion. Furthermore, some scanners utilize liquid lenses with dynamically adjustable focus to achieve a larger scanning range, such as those described in Chinese Invention Patent Application No. CN202510357685.3. This solution is costly, requires additional assembly of components such as circuit boards, and has reliability issues with liquid lenses. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an autofocus lens with large depth of field, high resolution, small distortion, high focusing accuracy and small size.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: an autofocus lens with a large depth of field and high resolution, which is composed of a front lens group with positive focal power, an aperture, a middle lens group with positive focal power, and a rear lens group with negative focal power, from the object plane to the image plane. The aperture and the middle lens group are driven by a voice coil motor to move synchronously back and forth along the optical axis to achieve autofocus. The focal length f1 of the front lens group is: 15mm≤f1≤27mm, the focal length f2 of the middle lens group is: 8mm≤f2≤10mm, and the focal length f3 of the rear lens group satisfies: 5mm≤|f3|≤6mm. The focal length of the autofocus lens is f, and satisfies: 1.2≤|f1 / f|≤2.2, 0.6≤|f2 / f|≤0.9, 0.4≤|f3 / f|≤0.6. The total optical length TTL of the autofocus lens satisfies: 16mm≤TTL≤20mm, and the working F# satisfies: 3≤F#≤4.

[0006] Compared with existing technologies, the advantages of this invention lie in its autofocus design, which utilizes a voice coil motor to drive the synchronous movement of the diaphragm and the center lens group along the optical axis, achieving a large depth of field. By optimizing the focal length and selecting specific optical parameters, the autofocus lens achieves high resolution and low distortion. Combined with the voice coil motor, it effectively reduces the size of the lens and reduces costs while still achieving high-quality imaging across a wide depth of field. Compared to traditional autofocus lenses and liquid autofocus lenses, the autofocus lens of this invention offers higher resolution, a smaller size, improved autofocus accuracy, and a greater depth of field.

[0007] Preferably, the distance that the voice coil motor drives the aperture and the middle lens group to synchronously move forward and backward along the optical axis is 0.4 mm to 0.55 mm.

[0008] Preferably, the front lens group comprises a first lens with positive optical power, the middle lens group comprises a second lens with negative optical power and a third lens with positive optical power, and the rear lens group comprises a fourth lens with negative optical power, a fifth lens with positive optical power, and a sixth lens with negative optical power. The six-lens optical structure effectively reduces lens size and costs.

[0009] Preferably, the object-side surface of the first lens is convex, the image-side surface of the second lens is concave, the object-side surface and the image-side surface of the third lens are both convex, the object-side surface of the fourth lens is convex, and the image-side surface is concave; the image-side surface of the fifth lens is convex; and the object-side surface of the sixth lens is concave, and the image-side surface is convex.

[0010] Preferably, the refractive index Nd1 of the first lens is greater than 1.6. Selecting a high refractive index material can better collect light entering the autofocus lens, which is beneficial to improving the long-distance imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Schematic diagram of the structure of the auto-focus lens in Embodiment 1 of the present invention;

[0012] Figure 2 This is a transfer function curve diagram of Example 1 of the present invention at an object distance of 300 mm;

[0013] Figure 3 This is a transfer function curve diagram of Example 1 of the present invention at an object distance of 150 mm;

[0014] Figure 4 This is a transfer function curve diagram of the first embodiment of the present invention at infinite object distance;

[0015] Figure 5 This is a distortion diagram of Example 1 of the present invention at an object distance of 300 mm;

[0016] Figure 6 Schematic diagram of the structure of the auto-focus lens in the second embodiment of the present invention;

[0017] Figure 7 This is a transfer function curve diagram of Example 2 of the present invention at an object distance of 300 mm;

[0018] Figure 8 This is a transfer function curve diagram of Example 2 of the present invention at an object distance of 150 mm;

[0019] Figure 9 This is a transfer function curve diagram of the second embodiment of the present invention at infinite object distance;

[0020] Figure 10 This is a distortion diagram of Example 2 of the present invention at an object distance of 300mm;

[0021] Figure 11 Schematic diagram of the structure of the auto-focus lens in the third embodiment of the present invention;

[0022] Figure 12 This is a transfer function curve diagram of Example 3 of the present invention at an object distance of 300 mm;

[0023] Figure 13 This is a transfer function curve diagram of Example 3 of the present invention at an object distance of 150 mm;

[0024] Figure 14 This is a transfer function curve diagram of embodiment 3 of the present invention at infinite object distance;

[0025] Figure 15 This is a distortion curve diagram of Example 3 of the present invention at an object distance of 300 mm.

[0026] Description of reference numerals:

[0027] 100, front lens group; STO, aperture; 200, middle lens group; 300, rear lens group; L1, first lens; L2, second lens; L3, third lens; L4, fourth lens; L5, fifth lens; L6, sixth lens; IMA, image plane. DETAILED DESCRIPTION

[0028] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0029] When describing each lens, the concavity and convexity of the lens surface is defined according to the curvature radius R value, that is, when the curvature radius R value of the object side of the lens is positive, the object side surface is convex, otherwise it is concave; when the curvature radius R value of the image side of the lens is positive, the image side surface is concave, otherwise it is convex.

[0030] The present invention provides an autofocus lens with a large depth of field and high resolution. The lens is composed of a front lens group 100 with positive focal length, an aperture STO, a middle lens group 200 with positive focal length, and a rear lens group 300 with negative focal length, from the object plane to the image plane IMA. The aperture STO and the middle lens group 200 are driven by a voice coil motor to move synchronously forward and backward along the optical axis to achieve autofocus. The range of the ... , the focal length f2 of the middle lens group 200 is: 8mm≤f2≤10mm, the focal length f3 of the rear lens group 300 satisfies: 5mm≤|f3|≤6mm, the focal length of the autofocus lens is f, and satisfies: 1.2≤|f1 / f|≤2.2, 0.6≤|f2 / f|≤0.9, 0.4≤|f3 / f|≤0.6, the total optical length TTL of the autofocus lens satisfies: 16mm≤TTL≤20mm, and the working F number F# satisfies: 3≤F#≤4.

[0031] like Figure 1 、 Figure 6 and Figure 11As shown, in order to effectively reduce the volume of the autofocus lens and reduce the cost, the present invention adopts a six-piece optical structure. The front lens group 100 is the first lens L1 with positive focal length. In order to better collect light entering the autofocus lens, the first lens L1 is made of a high refractive index material with a refractive index Nd1 greater than 1.6, which is conducive to improving the long-range imaging quality; the middle lens group 200 is composed of the second lens L2 with negative focal length and the third lens L3 with positive focal length. The rear lens group 300 is composed of the fourth lens L2 with negative focal length. The lens is composed of a front lens group 100, a fifth lens group L4, a positive optical power lens group L5, and a sixth lens group L6 with negative optical power. The object-side surface of the first lens group L1 is convex, the image-side surface of the second lens group L2 is concave, and both the object-side and image-side surfaces of the third lens group L3 are convex. To further control the direction of light in each field of view, the light is diverged and then converged to form an image on the image plane IMA; the object-side surface of the fourth lens group L4 is convex, and the image-side surface is concave; the image-side surface of the fifth lens group L5 is convex; and the object-side surface of the sixth lens group L6 is concave, and the image-side surface is convex. To reduce the volume of the entire lens and improve relative illumination, an aperture stop STO is placed between the front lens group 100 and the middle lens group 200.

[0032] The accuracy of the voice coil motor is less than 2um, preferably 1um, which can improve the focusing accuracy of the autofocus lens.

[0033] Furthermore, in order to effectively reduce the number of lenses, reduce the size of the lens, and better correct aberrations, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are all aspherical lenses, and their surface shapes satisfy the following equations:

[0034]

[0035] Among them, y represents the radial coordinate value of the lens perpendicular to the optical axis, Z(y) is the sagittal height of the aspheric lens at a height of y along the optical axis from the aspheric vertex, c=1 / R, R represents the curvature radius corresponding to the center of the aspheric lens surface, k represents the cone coefficient, and the parameters are A 、 B 、 C 、 D 、 E These are the coefficients of the 2nd, 4th, 6th, 8th, and 10th order terms of the high-order aspheric polynomial.

[0036] The object-side and image-side surfaces of the second lens L2 and the third lens L3 are both aspherical, which can control the angles of light rays in different fields of view and reduce aberrations caused by light beam collection.

[0037] The object-side and image-side surfaces of the fourth lens L4 are aspherical, with smoother center and edges, which can control the angle of light and make it transition slowly to the next surface, reducing distortion, coma, astigmatism and spherical aberration.

[0038] The object-side and image-side surfaces of the fifth lens L5 and the sixth lens L6 are both aspherical, which can control the angles of light rays in different fields of view and significantly reduce distortion.

[0039] The scanning lens of the present invention will be described in detail below with reference to specific embodiments.

[0040] Example 1: The structure of the large depth of field and high resolution autofocus lens of this example 1 is as follows: Figure 1 As shown, it consists of a front lens group 100 with positive focal power, an aperture STO, a middle lens group 200 with positive focal power, and a rear lens group 300 with negative focal power, which are sequentially arranged from the object plane to the image plane IMA.

[0041] The front lens group 100 is a first lens L1 with positive refractive power, a convex object-side surface and a concave image-side surface.

[0042] The middle lens group 200 consists of a second lens L2 with negative optical power and a third lens L3 with positive optical power. The second lens L2 is a biconcave lens, and the third lens L3 is a biconvex lens.

[0043] The rear lens group 300 consists of a fourth lens L4 with negative optical power, a fifth lens L5 with positive optical power, and a sixth lens L6 with negative optical power. The object-side surface of the fourth lens L4 is convex and the image-side surface is concave. The object-side surface of the fifth lens L5 is concave and the image-side surface is convex. The sixth lens L6 is a meniscus lens with a concave object-side surface and a convex image-side surface.

[0044] The specific parameters of Example 1 are shown in Table 1:

[0045] Table 1

[0046]

[0047] Wherein, D1 represents the distance between the image side surface of the front lens group 100 and the aperture, and D2 represents the distance between the image side surface of the middle lens group 200 and the object side surface of the rear lens group 300. The specific values ​​are shown in Table 2:

[0048] Table 2

[0049]

[0050] The high-order coefficients of the aspheric lens in this embodiment are shown in Table 3 ( A : 2nd order coefficient, B : 4th order coefficient, C : 6th order coefficient, D : 8th order coefficient, E : 10th order coefficient):

[0051] Table 3

[0052]

[0053] The main design parameters of this embodiment 1 are shown in Table 4:

[0054] Table 4

[0055]

[0056] In the first embodiment, the transfer function curves of the autofocus lens at object distances of 300 mm, 150 mm, and infinity are shown as follows: Figure 2 、 Figure 3 and Figure 4 As shown, the meridian and sagittal lines at 0mm coincide; the distortion curve of the autofocus lens at 300mm is as follows Figure 5 shown.

[0057] Figure 2 、 Figure 3 and Figure 4 The transfer function curve shown in the figure shows that in the first embodiment, at 200 lp / mm, the MTF at an object distance of 300 mm is greater than 0.35, the MTF at an object distance of 150 mm is greater than 0.30, and the MTF at an infinite object distance is greater than 0.25.

[0058] Figure 5 The distortion curve shown shows that the distortion of the first embodiment is less than 1.4%.

[0059] Example 2: The structure of the large depth of field and high resolution autofocus lens of Example 2 is as follows: Figure 6 As shown, the basic structure is the same as that of the first embodiment, and only the total length of the lens is compressed by optimizing the lens focal length and the air space, thereby optimizing the aberration, improving the resolution, and reducing the distortion.

[0060] The optical system is composed of a front lens group 100 with positive focal power, an aperture STO, a middle lens group 200 with positive focal power, and a rear lens group 300 with negative focal power, which are sequentially arranged from the object plane to the image plane IMA.

[0061] The front lens group 100 is a first lens L1 with positive refractive power, a convex object-side surface and a concave image-side surface.

[0062] The middle lens group 200 consists of a second lens L2 with negative optical power and a third lens L3 with positive optical power. The second lens L2 is a biconcave lens, and the third lens L3 is a biconvex lens.

[0063] The rear lens group 300 consists of a fourth lens L4 with negative optical power, a fifth lens L5 with positive optical power, and a sixth lens L6 with negative optical power. The object-side surface of the fourth lens L4 is convex and the image-side surface is concave. The object-side surface of the fifth lens L5 is convex and the image-side surface is convex. The sixth lens L6 is a meniscus lens with a concave object-side surface and a convex image-side surface.

[0064] The specific parameters of Example 2 are shown in Table 5:

[0065] Table 5

[0066]

[0067] Wherein, D1 represents the distance between the image side surface of the front lens group 100 and the aperture, and D2 represents the distance between the image side surface of the middle lens group 200 and the object side surface of the rear lens group 300. The specific values ​​are shown in Table 6:

[0068] Table 6

[0069]

[0070] The high-order coefficients of the aspheric lens in this embodiment 2 are shown in Table 7 ( A : 2nd order coefficient, B : 4th order coefficient, C : 6th order coefficient, D : 8th order coefficient, E : 10th order coefficient):

[0071] Table 7

[0072]

[0073] The main design parameters of the second embodiment are shown in Table 8:

[0074] Table 8

[0075]

[0076] In the second embodiment, the transfer function curves of the autofocus lens at object distances of 300mm, 150mm and infinity are shown as follows: Figure 7 、 Figure 8 and Figure 9 As shown, the meridian and sagittal lines at 0mm coincide; the distortion curve of the autofocus lens at 300mm is as follows Figure 10 shown.

[0077] Figure 7 、 Figure 8 and Figure 9 The transfer function curve shown in the figure shows that in the second embodiment, at 200 lp / mm, the MTF at an object distance of 300 mm is greater than 0.39, the MTF at an object distance of 150 mm is greater than 0.3, and the MTF at an infinite object distance is greater than 0.3.

[0078] Figure 10 The distortion curve shown shows that the distortion of the second embodiment is less than 0.5%, which is a significant decrease compared to the first embodiment.

[0079] Example 3: The structure of the large depth of field and high resolution autofocus lens of Example 3 is as follows: Figure 11 As shown, the third embodiment is based on the first embodiment, and mainly changes the optical power of the sixth lens. By optimizing the optical power, surface shape and air space of the lens, the total length of the lens is compressed, the aberration is optimized, the resolution is improved, and the distortion is reduced.

[0080] The front lens group 100 includes a first lens L1 having positive refractive power, and the first lens L1 is a biconvex lens.

[0081] The middle lens group 200 is composed of a second lens L2 with negative optical power and a third lens L3 with positive optical power. The object side surface of the second lens is convex and the image side surface is concave. The third lens L3 is a biconvex lens.

[0082] The rear lens group 300 consists of a fourth lens L4 with negative optical power, a fifth lens L5 with positive optical power, and a sixth lens L6 with negative optical power. The object side surface of the fourth lens L4 is convex and the image side surface is concave. The object side surface of the fifth lens L5 is concave and the image side surface is convex. The sixth lens L6 is a meniscus lens with a concave object side surface and a convex image side surface.

[0083] The specific parameters of Example 3 are shown in Table 9:

[0084] Table 9

[0085]

[0086] Wherein, D1 represents the distance between the image side surface of the front lens group 100 and the aperture, and D2 represents the distance between the image side surface of the middle lens group 200 and the object side surface of the rear lens group 300. The specific values ​​are shown in Table 10:

[0087] Table 10

[0088]

[0089] The high-order coefficients of the aspheric lens in this embodiment 3 are shown in Table 11 ( A : 2nd order coefficient, B : 4th order coefficient, C : 6th order coefficient, D : 8th order coefficient, E : 10th order coefficient):

[0090] Table 11

[0091]

[0092] The main design parameters of this embodiment 3 are shown in Table 12:

[0093] Table 12

[0094]

[0095] In the third embodiment, the transfer function curves of the lens at object distances of 300mm, 150mm and infinity are shown as follows: Figure 12 、 Figure 13 and Figure 14 As shown, the meridian and sagittal lines at 0mm coincide; the distortion curve of the lens at 300mm is as follows Figure 15 shown.

[0096] Figure 12 、 Figure 13 and Figure 14 The transfer function curves shown in the figure show that the MTF of the third embodiment is greater than 0.4 at 200 lp / mm at object distances of 300 mm, 150 mm, and infinity. Compared with the first and second embodiments, the MTF of the entire field of view is improved.

[0097] Figure 15 The distortion curve shown shows that the distortion of the third embodiment is less than 1.9%.

[0098] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An autofocus lens with a large depth of field and high resolution, characterized in that: From the object plane to the image plane, it is composed of a front lens group with positive focal power, an aperture, a middle lens group with positive focal power, and a rear lens group with negative focal power. The front lens group is a first lens with positive focal power, the middle lens group is composed of a second lens with negative focal power and a third lens with positive focal power, the rear lens group is composed of a fourth lens with negative focal power, a fifth lens with positive focal power, and a sixth lens with negative focal power. The aperture and the middle lens group are driven by a voice coil motor to move synchronously forward and backward along the optical axis to achieve autofocus. The focal length of the front lens group is f1 The focal length f2 of the middle lens group satisfies: 8mm≤f2≤10mm, the focal length f3 of the rear lens group satisfies: 5mm≤|f3|≤6mm, the focal length of the autofocus lens is f, and satisfies: 1.2≤|f1 / f|≤2.2, 0.6≤|f2 / f|≤0.9, 0.4≤|f3 / f|≤0.6, the total optical length TTL of the autofocus lens satisfies: 16mm≤TTL≤20mm, and the working F number F# satisfies: 3≤F#≤4.

2. The autofocus lens with large depth of field and high resolution according to claim 1, wherein: The voice coil motor drives the aperture and the middle lens group to move synchronously forward and backward along the optical axis, and the distance is 0.4mm to 0.55mm.

3. The autofocus lens with large depth of field and high resolution according to claim 1, wherein: The object side surface of the first lens is convex, the image side surface of the second lens is concave, the object side surface and the image side surface of the third lens are both convex, the object side surface of the fourth lens is convex, and the image side surface is concave; the image side surface of the fifth lens is convex; and the object side surface of the sixth lens is concave, and the image side surface is convex.

4. The autofocus lens with large depth of field and high resolution according to claim 3, wherein: The refractive index Nd1 of the first lens is greater than 1.6.

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